The invention relates to a compressed air motor comprising a housing having a guide bore and a rotor rotatably mounted therein, the rotor being provided with slots which run outwards and in which plate-like vanes are mounted so as to be radially displaceable by the centrifugal force, and a substantially cylindrical, freely rotatable sleeve which covers the outside of the vanes is arranged in the region of the vanes between the outside of the rotor and the guide bore of the housing.
The prior art recognizes various types of vane motors which are operated with compressed air. European Patent EP-B1-394651 describes a design comprising a rotor and vanes displaceable by centrifugal force, the rotor being arranged in a rotatable sleeve which is housed inside a bore of a housing.
This rotatable sleeve has the function of preventing the vanes from shearing against the inner surface of the housing. During operation, the rotor and the rotatable sleeve therefore rotate.
In this known design, the bore of the housing is not cylindrical but is non-cylindrically deformed on one side by a pocket. This is because it was evidently thought that feeding of compressed air into the space between the rotatable sleeve and the outer cylinder wall is required. Another reason is that the deformation on one side on the outside of the cylinder has presumably been required because there was also a tendency to lateral displacement of the rotatable sleeve due to the pressure load of the compressed air flowing axially into the space between the rotor and the rotatable sleeve, which lateral displacement could be compensated by the additional radial play in the recess.
The non-central formation of the bore in the housing results not only in greater manufacturing costs but also in an air loss during operation, which manifests itself in a low efficiency.
In U.S. Pat. No. 4,197,061, Boeing has disclosed a compressed air motor which manages without eccentric recesses in the housing bore but provides separate air-conveying channels on the inner surface of the housing which are supplied by means of compressed air and thus fill the space between the rotatable sleeve and housing with compressed air. The manufacture of these additional channels is, however, very complicated and interrupts the cylindrical formation of the housing bore, which can likewise lead to lower performance.
A further document of the prior art, U.S. Pat. No. 4,648,819 describes a pump which likewise has a rotatable sleeve. This rotatable sleeve is provided on its outside with various types of grooves which are intended to serve for conveying the medium to be pumped. The production of the grooves—extending partly over the circumference of the sleeves—on rotatable sleeves which themselves are composed only of a relatively thin-walled material is a relatively complicated measure. This known design gives no instructions at all regarding the manufacture of a compressed air motor.
U.S. Pat. No. 4,616,985 discloses a compressed air compressor which has vanes radially displaceable in a rotor and a sleeve surrounding said vanes and having orifices. The sleeve consists of a light metal alloy. The compressed air compressor has a relatively low speed and there therefore tends to be few problems with regard to wear.
The compressed air motors stated in the prior art and having a rotatable sleeve should—as already mentioned—in particular reduce the friction which occurs between the vanes and the outer housing in other compressed air motors and thus permit oil-free operation.
Particularly in the case of devices which are to be used in the area of surgery, it is important to be able to offer compressed air motors without oil lubrication, since no lubricating oil at all is permitted to enter the human body. Owing to their high speeds (up to about 80,000 rpm), compressed air motors used in surgery are difficult to seal in such a way that no leakage air losses and, associated therewith, oil emergence from the compressed air motor occur.